The present invention relates essentially to a self-contained workpiece-holding device, such as a plate, preferably including an operating system and advantageously provided with individual power-cylinder operating means for operating it at an independent pressure.
The presently known workpiece-holding plates are provided with means of fastening by tightening, clamping or the like of the said workpiece through the medium of compressed-fluid power-cylinders incorporated in the said plate and fed from a fluid-pressure generator actuated by a source of power.
In all the presently known workpiece-holding plates, the fluid-pressure generator as well as the source of power are arranged separately from the workpiece-holding plate and even, in some cases, outside the machining set. The fluid-pressure generator feeds the fastening means through flexible pipes connecting the pressure generator to the fastening means.
However, these known solutions suffer from the major drawback of an encumbering of the space by the passage of the flexible pipes which may be inadvertently deteriorated or cut.
Furthermore, the separate arrangement of the fluid-pressure generator and of the source of power increases the space occupied by the machining set.
In another respect, use is made in the known operating systems for the workpiece-holding devices of paths for the transmission of orders or commands from an external control device, which are constituted by physical links such as electric wires or cables. It is easily understood that the presence of such wires or cables is inconvenient, especially when the number of the workpiece-holding devices is relatively important.
Lastly, in these known workpiece-holding devices, all the power-cylinders are fed simultaneously at the same pressure, which has the major disadvantage of also leading to a simultaneous freeing of the pressure in all the power-cylinders. Furthermore, such operation at a single pressure requires the use, as power means, of single-acting cylinders.